Technical Field
The present invention relates generally to an abrading structure (such as a construct), and more particularly to the making of an abrading structure including impregnated diamond.
Description of Related Art
Prior art impregnated diamond structures (also known as constructs) are made using a random distribution of grit or small carat weight diamond granules within a cell of tungsten carbide powder. The diamond may be natural or synthetic. A hot isostatic pressing, sintering or binder infiltration process is then performed to fuse the tungsten carbide powder and retain the randomly distributed diamond. The resulting structure, which is sometimes referred to in the art as a diamond impregnated construct or segment, may then be used in an abrading tool. One example of such an abrading tool is an earth boring drill bit which is constructed by casting the constructs into a drill bit body, or alternatively attaching the constructs (using, for example, a brazing process) to the drill bit body. In other abrading applications, the constructs may be formed (by casting or attaching processes) to a tool body for use in grinding, abrading or other machining operations.
As a specific example, diamonds are mixed with matrix powder and binder into a paste-like material. The commonly known powder metallurgy process is used where the matrix powder comprises a mixture of tungsten and tungsten carbide and the binder material is a copper alloy. The paste is formed in a mold to a desired shape of the construct, and heat is applied to support binder infiltration and formation of the construct. Within the construct, the included diamond is suspended near and on the external surface of the construct and is randomly distributed. Such a random distribution, however, implies an irregular diamond distribution including areas with diamond clusters, areas of lower diamond concentration, and even areas that are void of diamond content.
Historically, the random distribution of diamond content within impregnated diamond constructs was viewed as desirable. The reason for this was that fresh cutting diamond was constantly being exposed as the fused tungsten carbide matrix surrounding the diamond particles was worn away during the abrading, grinding, machining, or cutting process for which the construct was being used. However, areas of the construct with diamond clusters may lack sufficient matrix material to support diamond retention during tool operation, while areas of low or no diamond content tend to exhibit poor wear properties. Additionally, constant exposure of fresh cutting diamond allows for an accompanying random distribution of matrix material striations trailing behind the exposed diamond particles. This results in a clogged interface between the construct and the surface of the target material (such as a rock formation in an earth drilling application). These striations also limit the depth of cut, and thereby slow penetration of the construct into the work target. The striations further reduce the ability of cooling fluids to carry heat away from the workface. Excess heat build-up at the workface tends to accelerate diamond failure and wear of the tungsten carbide matrix. Thus, it is now understood that the failure of prior art constructs with randomly distributed diamond is a direct result of the presence of that randomly distributed diamond in the construct.
There is a need in the art for an improved diamond construct which addresses the foregoing, and other, problems experienced with the making and use of randomly distributed impregnated diamond constructs.